This invention relates to a variable venturi carburetor for an internal combustion engine which may suppress fluctuation in air-fuel ratio by preventing vaporization of fuel at engine idle operation.
In recent years, as a part of development of automobiles having good fuel economy, there has been significant development of reducing fuel consumption wherein the engine is run stably with leaner air-fuel ratio at idle operation and yet with lower idling engine speeds. In a conventional variable venturi carburetor, when temperature of the carburetor body rises after running of the engine at high speeds, temperature of the main fuel jet in the carburetor body also rises and fuel temperature in the fuel well in the main fuel jet rises to create fuel vapor. The fuel vapor influences fuel metering operation at the main fuel jet or it is mixed with air/fuel mixture in the air intake passage, thus fluctuating the air-fuel ratio. Particularly, at idle engine operation at low idling speeds and with leaner air-fuel ratio, fuel combustion condition becomes unstable, and it sometimes causes engine stall.